This is a bit longwinded, so apologies: I tried sculpting because I saw a video on YouTube where this guy, I think he goes by Craftyart, or Craftyarts - he had a speed video where he sculpted, cast, and painted a version of the Joker, but it was Willem DaFoe. It was incredible, and it just gave me an itch. I watched it and wanted to do that, to make that.
For me, I'd often have these ideas of things I wanted to try, or do, or challenge myself with, and then for some inexplicable reason I'd never do them. In this instance, I told myself to get off my ass and just give it a try. It may have helped that I was in therapy at the time and making efforts to address a lifetime of issues. It has lent a certain proactiveness to my being. For me, addressing my mental health is a driving factor in having made any of this possible.
Finding a seed of interest: if you mean directly with making a costume, I don't know. If you're not interested in costumes, I don't think it is something you can force. Overall though I think anything that causes that itch, that pull, maybe even a sense of yearning "to do" is enough to get you going on a path. I had a feeling when watching the video that reminded me of what I felt when I was a kid and I would see something and I'd get excited to do the same.
I don't know that any of this would have come together for me had I not been on a journey to improve my mental health, and making efforts to find something that connected with me. Something outside of a screen. But in the end, what I connected with was surprising. It looks like it makes sense in hindsight, but at that time, it felt like it came out of left field.
Hopefully there are some tips somewhere in this mess of words. If not, my apologies for wasting your time.